1. Related Applications
This application relates to contemporaneously filed applications Ser. No. 09/548,922, entitled "Constant Displacement Oil Web System and Method of Operating the Same", and Ser. No. 09/548,922, entitled "Multi-Level Oiling Device Drive Mechanism", both of which are expressly incorporated herein by reference.
2. Field of the Invention
The present invention relates to an electrophotographic imaging apparatus, and more particularly to a fuser oiling apparatus and the associated method involved with its use and operation.
3. Description of the Related Art
In an imaging apparatus, such as a laser printer using the electrophotographic process, an electrostatic image is created upon a photosensitive member, such as a roll or belt. Visible electroscopic marking particles, commonly referred to as toner, are applied to the electrostatic image on the photosensitive material. Thereafter, the toner is transferred to the desired media, which may include paper, transparency sheets or the like.
The toner image applied to the media is not permanent, however, until the toner is fixed by the application of heat. The toner is elevated in temperature sufficiently to cause constituents of the toner to become tacky, and flow into the pores or interstices between fibers of the media. Upon cooling, the toner again solidifies, causing the toner to adhere to the media. Pressure may be applied to enhance the flow of the toner, and thereby improve the subsequent bonding of the toner to the media.
Thermally fixing the electroscopic toner images commonly has been accomplished by passing the media, with the toner image thereon, through a nip formed by opposed rolls, at least one of which is heated internally. The heated roll, transferred thereafter elsewhere in the apparatus. The presence of wayward toner particles in the imaging apparatus can degrade the quality of the printed sheets.
To reduce sticking and toner offset to the fuser roll, fusers of the type described above commonly employ an apparatus for applying a release fluid to the surface of the fuser roll. The release fluid creates a weak boundary between the heated roll and the toner, thereby substantially minimizing the offset of toner to the fuser roll, which occurs when the cohesive forces in the toner mass are less than the adhesive forces between the toner and the fuser roll. Silicone oils having inherent temperature resistance and release properties suitable for the application are commonly used as release fluids. Polydimethylsiloxane is one such suitable silicone oil that has been used advantageously in the past.
Several methods and apparatuses have been used to supply oil to the fuser hot roll, including oil wicking systems, oil delivery rolls and oil webs. Oil wicking systems include reservoir tanks of the desired release agent or oil, and a piece of fabric wick material having one end mounted in the reservoir and the other end spring biased against the hot roll. Oil from the reservoir is drawn through the fabric wick by capillary action, and is deposited against the roll surface. While a wicking system can be effective in supplying oil to the fuser roll, surface deposit of the oil on the roll can be inconsistent, and the replenishment or replacement of the oil and/or system can be difficult and messy. Further, oil wicking systems can be designed only for a single oil delivery rate, determined by the rate of capillary action of the oil through the wick. By necessity, the delivery rate must be for the maximum oil demand for the print processes to be performed, and the media types to be used in the imaging apparatus. This can result in the over-application of oil under some conditions.
Oil delivery roll systems used in the past commonly include a roll nipped against the hot fuser roll, and either freely rotating against the fuser roll or driven against the fuser roll through a gear train. Oil delivered to the surface of the oil delivery roll is deposited on the hot fuser roll as the rolls rotate against each other. Various structures have been used for providing oil to the surface of the oil delivery roll, including reservoirs at the center of the roll, which may include a hollow tube filled with oil, providing oil to the surface through small tubes or via capillary action through the outer material. Felts or metering membranes may be used in the oil delivery roll to control the oil flow through the roll. Another style of oil delivery roll, referred to as a web-wrapped roll, includes high temperature paper or non-woven material saturated with oil, and wrapped around a metal core. Similarly to oil wicking systems, oil delivery rolls can be designed for a single delivery rate only, and can create excessive oil application under some operating conditions of the imaging apparatus.
Conventional oil web systems include a supply spool of web material, generally being a fabric of one or more layers saturated with the desired oil. Commonly, the web material is a non-woven fabric of polyester and aramid fibers, such as Nomex.RTM. manufactured by DuPont. A take-up spool is provided for receiving the used web. A web path, commonly including one or more guide rolls, extends from the supply spool to the take-up spool. A portion of the web path brings the web material into contact with the hot fuser roll, either by wrapping a portion of the web around the hot roll, or by utilizing a spring- loaded idler roll to nip the web material against the fuser roll. As the fuser roll rotates against the web in contact therewith, oil is transferred from the web to the fuser roll. Periodically, a drive mechanism for the take-up spool activates, rotating the spool and advancing web material from the supply spool to the take-up spool, thereby bringing a fresh section of web material into contact with the fuser roll.
Such conventional oil web systems can be used to deliver oil at a relatively constant rate with good uniformity. However, the oil flow is dependent on the amount of material brought into contact with the fuser roll over a given period of time. In oil web systems utilized heretofore, the simplified drive systems for the take-up roll have been operated for consistent durations at constant intervals throughout the life of the web system. Therefore, as spent material passes onto the take-up spool, and the diameter of the take-up spool increases, the linear length of material brought into contact with the fuser roll increases during each web advancement, thereby increasing the amount of oil deposited on the fuser roll.
An improved oil web system is described in our co-pending patent application entitled "Constant Displacement Oil Web System, And Method For Operating The Same" filed on even date herewith. In the improved system described therein, the problem of the incremental increase in the linear advancement of the web as the take-up spool diameter increases has been solved by adjustment of the drive mechanism operating cycle. However, the oil web system described therein also provides only a single oil application rate, regardless of the media type being printed. The design oil application rate must meet the maximum demand for oil required by the imaging apparatus design parameters, and can result in excess oil application under some conditions.
Excess oil on the fuser roll has undesirable effects. Since the paper passing through the fuser system generally carries away a portion of the oil deposited on the fuser roll, an excess amount of oil on the fuser roll, when picked up by the paper or other media, can cause an undesirable glossy appearance to the media. In duplexing systems, oil carried on the first printed side can be transferred to other areas of the imaging apparatus, when the media passes again through the apparatus for printing on the second side. Excessive amounts of oil deposited in other sections of the imaging apparatus can decrease print quality and otherwise produce undesirable operating effects. Additionally, unnecessary advancement of the web is wasteful, and shortens the useful life of the oiling system, necessitating replacement.
While excessive amounts of oil can result in problems and difficulties as mentioned above, controlling the amount of oil applied to the fuser roll can alter the appearance of the image on the printed sheet. It is often desirable that the printed image has glossiness similar to the glossiness of the media on which it is printed. Glossiness of the toner image is partially determined by the ease of release of the toner from the fuser roll. Therefore, if slightly more oil is applied to the fuser roll, a higher gloss can be achieved for the printed image as release of the toner from the fuser roll would be enhanced, and roughness of the toner image would be minimized. Conversely, if a duller or matte appearance is desired for the printed image, the use of slightly less oil on the fuser roll would result in a slightly increased tendency of the toner to adhere to the fuser roll, thereby creating the matte or dull look to the print. However, an adjustable oiling apparatus to control glossiness has not been available heretofore.
What is needed is a multi-level oiling device for an imaging apparatus fuser drum in which the application rate of oil can be varied, to more closely meet the requirements of the imaging apparatus operating conditions. More specifically, what is needed is an oil web system for an imaging apparatus in which the indexing increment length and frequency of the oil web can be varied to meet release demands of the media being processed, or the user preferences for printed appearance of the media.